Front end components such as directional couplers and radio frequency (RF) multiplexers have numerous applications in devices such as cellular phones. For example, carrier aggregation provides increased bandwidth in modern 4G communication protocols in which a handset communicates over multiple component carriers. Each component carrier has a certain bandwidth centered about a corresponding center frequency. Although a 4G transmitter may thus communicate over different carrier components (and thus over different frequency bands), it is conventional that this communication occur through a common antenna (or antennas). For example, a transmitter may drive a low-pass channel corresponding to a lower frequency carrier component and also drive a mid-band channel corresponding to a higher frequency carrier component. The two channels couple through a diplexer (RF multiplexer) to drive the common antenna(s). In addition, the transmitter needs feedback information to control the power of the signals through the different frequency channels.
It is thus conventional to include a directional coupler for each channel as shown in FIG. 1 for a transmitter 100. The low-band (LB) channel includes an LB power amplifier (PA) module that drives a LB directional coupler 105 that in turn drives an RF multiplexer 115. RF multiplexer 115 may drive an antenna with the low-band signal from LB directional coupler 105. A coupled port from LB directional coupler 105 provides a feedback signal (LB_cp) that is an attenuated version of the directional coupler output—e.g., LB_cp may be attenuated by −20 dB as compared to the LB directional coupler output signal driving RF multiplexer 115. Transmitter 100 uses the low-band feedback signal LB_cp for power control of the LB band transmission. Similarly, a mid-band (MB) channel includes a MB PA module that drives an MB directional coupler 110 that in turn drives RF multiplexer 115 and ultimately the common antenna. MB directional coupler 110 provides a MB feedback signal (MB_cp) from its coupled port so that transmitter 100 may control the power of the MB signal.
Given the serial arrangement of LB directional coupler 105 to RF multiplexer 115, the insertion loss in the LB channel is thus a sum of the insertion loss from LB directional coupler 105 and also RF multiplexer 115. Similarly, the insertion loss in the MB channel is a sum of the insertion loss from MB directional coupler 110 and RF multiplexer 115. In addition, the three separate components (the pair of directional couplers and RF multiplexer) demand a significant amount of die space.
Accordingly there is a need in the art for directional couplers and RF multiplexers providing increased density and lower insertion loss.